1. Field of the Invention
The present invention relates to data storage libraries housing multiple tapes or other data storage cartridges in various slots. More particularly, the invention concerns a data storage library that efficiently utilizes physical input/output (xe2x80x9cI/Oxe2x80x9d) slots by using functional addresses to conduct virtual cartridge ejects to the I/O slots.
2. Description of the Related Art
Many data processing systems require a large amount of data storage, for use in efficiently accessing, modifying, and re-storing data. Data storage is typically separated into several different levels, each level exhibiting a different data access time or data storage cost. A first, or highest level of data storage involves electronic memory, usually dynamic or static random access memory (xe2x80x9cDRAMxe2x80x9d or xe2x80x9cSRAMxe2x80x9d). Electronic memories take the form of semiconductor integrated circuits where millions of bytes of data can be stored on each circuit, with access to such bytes of data measured in nanoseconds. The electronic memory provides the fastest access to data since access is entirely electronic.
A second level of data storage usually involves direct access storage devices (xe2x80x9cDASDxe2x80x9d). DASD storage, for example, includes magnetic and/or optical disks. Data bits are stored as micrometer-sized magnetically or optically altered spots on a disk surface, representing the xe2x80x9conesxe2x80x9d and xe2x80x9czerosxe2x80x9d that comprise the binary value of the data bits. Magnetic DASD includes one or more disks that are coated with remnant magnetic material. The disks are rotatably mounted within a protected environment. Each disk is divided into many concentric tracks, or closely spaced circles. The data is stored serially, bit by bit, along each track. An access mechanism, known as a head disk assembly (xe2x80x9cHDAxe2x80x9d) typically includes one or more read/write heads, and is provided in each DASD for moving across the tracks to transfer the data to and from the surface of the disks as the disks are rotated past the read/write heads. DASDs can store gigabytes of data, and the access to such data is typically measured in milliseconds (orders of magnitudes slower than electronic memory). Access to data stored on DASD is slower than electronic memory due to the need to physically position the disk and HDA to the desired data storage location.
A third or lower level of data storage includes tapes, tape libraries, and optical disk libraries. Access to library data is much slower than electronic or DASD storage because a robot or human is necessary to select and load the needed data storage medium. An advantage of these storage systems is the reduced cost for very large data storage capabilities, on the order of Terabytes of data. Furthermore; tape storage is especially useful for backup purposes. That is, data stored at the higher levels of data storage hierarchy is reproduced for safe keeping on magnetic tape. Access to data stored on tape and/or in a library is presently on the order of seconds.
There are a number of different data storage libraries on the market today, including models made by International Business Machines (xe2x80x9cIBMxe2x80x9d). A number of today""s data storage libraries utilize the small computer system interface (xe2x80x9cSCSIxe2x80x9d) medium changer standard. This standard is xe2x80x9clocation-centricxe2x80x9d because it requires the host to manage cartridge movement by specifying source and destination locations in the system. Each location is a site capable of holding a cartridge, and is referred to as an xe2x80x9celement.xe2x80x9d Each element is given a fixed element address, either at the time of manufacture or at the time of system installation or configuration. The SCSI medium changer protocol defines four types of elements: medium transport element, storage element, import/export element, and data transfer element. In physical terms, the medium transport element is an accessor gripper, a storage element is a storage slot, an import/export element is a library I/O slot or pass-through slot, and a data transfer element is a removable media drive.
Moves from one element to another are requested on the SCSI interface. Typically, moves from one element to another element are the responsibility of SCSI initiator software, also called independent software vendor programming. This includes moves between the I/O slots and the storage slots.
Even though some data storage libraries enjoy considerable commercial success today, IBM engineers are continually seeking to improve the performance and efficiency of these systems. One area of possible focus concerns the manner in which the library ejects cartridges and receives inserted cartridges. When an operator wishes to load a number of cartridges into a library without disrupting the accessor motion, the operator inserts the cartridges into the I/O slots. However, data storage libraries only have a finite number of I/O slots for use in transferring cartridges to and from the library. Consequently, eject/insert operations are blocked if the I/O slots fill up, until the independent software vendor programming moves the inserted cartridges to storage slots using the SCSI interface.
In addition, many libraries are slow to transfer cartridges into the library from I/O slots because they rely on human operators to issue commands to the host using a library control panel. This is because the host is needed to supervise cartridge insertion operations by issuing appropriate commands to library robotics. This situation may be exacerbated if the host is located remotely from the library, since the operator (and library control panel) are located at the host, but the operator must physically insert or remove cartridges from I/O slots at the library. Accordingly, the process of adding a large number of cartridges may involve many trips between the library""s I/O station and the control panel.
Furthermore, when the independent software vendor programming needs to eject some cartridges by operator request or automatically, the operator must ensure there is an empty I/O slot for each cartridge. Otherwise, the attempt may be blocked, causing error, failure, or other delay. For these and other reasons, known data storage libraries are amenable to improvement.
Broadly, the present invention concerns a data storage library that efficiently utilizes I/O slots while maintaining software compatibility by using functional addresses to conduct virtual cartridge moves from storage slots to I/O slots. More particularly, a location-centric library host manages cartridge movement according to functional storage addresses and functional I/O addresses. In reality, the library has multiple cartridge receiving slots, which include physical I/O slots and physical storage slots. In contrast with the physical I/O slots and physical storage slots, functional I/O addresses and functional storage addresses are virtual locations used by the host in managing cartridge locations. Thus, host knowledge of cartridge locations is limited to their functional addresses. The library includes a library map that correlates functional addresses with physical addresses.
Initially, an eject command is received from the host. The eject command requests transfer of a cartridge from a source functional storage address to a target functional I/O address. In response to the eject command, irrespective of any physical movement of the cartridge, the library reports successful completion of the requested eject command to the host. The library first gives a functional I/O address to the physical storage slot containing the cartridge. When a physical I/O slot becomes available, the library physically moves the cartridge there and either correlates the cartridge""s functional I/O address with this physical I/O slot, or registers the cartridge""s functional I/O address as empty.
Accordingly, in one embodiment, the invention may be implemented to provide a method to manage eject operations in a data storage library. In another embodiment, the invention may be implemented to provide an apparatus, such as a data storage library, configured to manage eject operations as explained herein. In still another embodiment, the invention may be implemented to provide a signal-bearing medium tangibly embodying a program of machine-readable instructions executable by a digital data processing apparatus to perform operations for managing eject operations in a data storage library. Another embodiment concerns logic circuitry having multiple interconnected electrically conductive elements configured to perform operations in a data storage library as discussed herein.
The invention affords its users with a number of distinct advantages. For example, host workload is reduced because the host can direct ejection of a cartridge without waiting for physical ejection to complete, and regardless of whether a physical I/O slot is available at that time. As another advantage, the invention maintains broad software compatibility between the host and library controller. The invention also provides a number of other advantages and benefits, which should be apparent from the following description of the invention.